A photomask processing step is performed by the following method. A resist layer is formed on a photomask blank in which an optical film (hereinafter also called “thin film”) including a light shielding layer and a phase shift film is formed on a substrate, and a resist pattern is formed on the resist layer by irradiating the resist layer with electron beams. Further, the resist pattern is transferred to the above-mentioned light shielding layer and phase shift film by subjecting the shielding layer and the phase shift film to etching.
The resist pattern, which is formed by electron beam irradiation during the processing step, is required to be formed at an extremely accurate position. However, a generally used resist layer is an insulator, and hence accumulation of charges (charge-up) may occur in the resist layer. Then, the charge-up causes distortion of the electron beam radiated to the surface of the photomask blank. The distortion of the electron beam results in slight shift of a position of the resist pattern formed on the photomask, and hence the distortion becomes a cause of reduction in positional accuracy of the resist pattern.
In order to avoid this problem, there has been known a technology of forming an organic conductive layer on the surface of the resist layer (for example, see Patent Document 1). When a water-soluble material is selected for the organic conductive layer, the configuration in which the organic conductive layer is formed on the resist layer has an advantage in that the organic conductive layer can be removed by a developer.
Further, there has been proposed a technology of forming an aluminum film or a metal conductive film on the surface of the resist layer formed on a wafer substrate (for example, see Patent Document 2).